In a polymer electrolyte fuel cell, a fuel gas such as hydrogen and an oxidant gas such as air are electrochemically reacted in an anode and a cathode serving as gas diffusion electrodes, respectively, thereby to generate electricity and heat at the same time. FIG. 10 shows a schematic exploded sectional view of a main part of the general basic configuration of such a polymer electrolyte fuel cell. A fuel cell 100, as shown in FIG. 10, comprises at least one unit cell mainly including a membrane electrode assembly (MEA) 105, and a pair of plate-shaped separators sandwiching the membrane electrode assembly 105, namely, an anode-side separator 106a and a cathode-side separator 106b. 
The membrane electrode assembly 105 has a configuration such that a polymer electrolyte membrane 101 for selectively transporting cations (hydrogen ions) is disposed between an anode 104a and a cathode 104b. Further, the anode 104a at least includes a catalyst layer 102a disposed in its polymer electrolyte membrane 101 side in a close contact manner, and a gas diffusion layer 103a disposed between the foregoing catalyst layer 102a and the anode-side separator 106a; and the cathode 104b at least includes a catalyst layer 102b disposed in its polymer electrolyte membrane 101 side in a close contact manner, and a gas diffusion layer 103b disposed between the foregoing catalyst layer 102b and the cathode-side separator 106b. 
The catalyst layers 102a and 102b are mainly composed of a conductive carbon powder carrying an electrode catalyst (e.g., platinum-group metal). The gas diffusion layers 103a and 103b have electric conductivity as well as gas permeability. The gas diffusion layers 103a and 103b are fabricated, for example, by forming a conductive water-repellent layer made of a conductive carbon powder and a fluorocarbon resin on a conductive porous base material made of carbon.
Here, as shown in FIG. 10, an MEA 105 is configured in such a manner that, in view of disposing gaskets 109a and 109b for preventing gas leakage, the main face of the polymer electrolyte membrane 101 is larger than the main faces of the anode 104a and the cathode 104b, and the polymer electrolyte membrane 101 is positioned such that its whole peripheral edge protrudes outside the peripheral edges of the anode 104a and the cathode 104b. Herein, the peripheral edge of the polymer electrolyte membrane 101 protruding outside the peripheral edges of the anode 104a and the cathode 104b is also referred to as a “protruding portion” (P in FIG. 10).
The anode-side separator 106a and the cathode-side separator 106b have electric conductivity, and serve to mechanically fix the MEA 105 as well as to electrically connect in series MEAs 105 adjacent to each other in the case where a plurality of MEAs 105 are stacked. Further, in the anode-side separator 106a and the cathode-side separator 106b, a fuel gas flow channel 107a and an oxidant gas flow channel 107b for supplying reaction gas to the anode 104a and the cathode 104b and carrying away gas including products produced by electrode reactions and unreacted reactants to the outside of the MEA 105 are formed in one face thereof (i.e., the main faces of the anode-side separator 106a and the cathode-side separator 106b, the faces being in contact with the anode 104a and the cathode 104b, respectively).
Further, in the other face of the anode-side separator 106a and the cathode-side separator 106b, cooling fluid flow channels 108a and 108b for introducing a cooling fluid (cooling water etc.) which serve to adjust the cell temperature at a substantially constant level are formed. By configuring such that the cooling fluid is circulated between the fuel cell and an externally arranged heat exchanger, heat energy generated by reaction can be utilized in a form of hot water etc.
The fuel gas flow channel 107a and the oxidant gas flow channel 107b are generally formed by providing grooves on one main face of the anode-side separator 106a and the cathode-side separator 106b, which is in contact with the anode 104a and the cathode 104b, respectively, for the reason that this can advantageously simplify the production process, and others. Further, the cooling fluid flow channels 108a and 108b are generally formed by providing grooves on the other main face of the anode-side separator 106a and the cathode-side separator 106b, which are facing to the outside.
In a so-called stacked fuel cell (fuel cell stack) obtained by electrically connecting a plurality of MEAs 105 in series with the anode-side separators 106a and the cathode-side separators 106b interposed between the plurality of MEAs 105, a manifold for dividing the flow of the reaction gas fed to the fuel cell to supply the gas to each MEA 105 (a manifold (not shown) formed by combining manifold apertures for supplying reaction gas in a continuously stacked manner, and manifold apertures for discharging reaction gas in a continuously stacked manner, the manifold apertures being provided in the anode-side separators 106a and the cathode-side separators 106b) is provided.
In addition, a manifold for dividing the flow of a cooling fluid fed to the fuel cell to supply the fluid to each MEA 105 (a manifold (not shown) formed by combining manifold apertures for supplying cooling fluid in a continuously stacked manner, and manifold apertures for discharging cooling fluid in a continuously stacked manner, the manifold apertures being provided in the anode-side separators 106a and the cathode-side separators 106b) is provided. The manifold formed in the interior of the fuel cell as described above is referred to as an internal manifold, and a typical fuel cell is such an “internal manifold type” fuel cell.
FIG. 11 shows a cross section taken along line III-III of FIG. 10 (i.e., a front view of the anode-side separators 106a in the conventional fuel cell 100 viewed from its fuel gas flow channel 107a side), a region of which being in contact with the anode-side gasket 109a is shown by hatching. Although not shown, a front view of the cathode-side separator 106b in the conventional fuel cell 100 viewed from its oxidant gas flow channel side 107b is similar to this.
As is shown in FIG. 11, the anode-side separator 106a is provided with a manifold aperture 114 for supplying fuel gas, a manifold aperture 115 for discharging fuel gas, a manifold aperture 118 for supplying cooling fluid, a manifold aperture 119 for discharging cooling fluid, a manifold aperture 116 for supplying oxidant gas, and a manifold aperture 117 for discharging oxidant gas. Likewise, the cathode-side separator 106b is provided with each manifold aperture.
Next, FIG. 12 is a cross section taken along line IV-IV of FIG. 10 (i.e., a front view of the conventional fuel cell 100 after the anode-side separator 106a is removed, viewed from its anode-side separator 106a side (before removal). Although not shown, a front view of the conventional fuel cell 100 after the cathode-side separator 106b is removed, viewed from its cathode-side separator 106b side (before removal) is similar to this.
In the conventional fuel cell 100, in order to prevent gas leakage of reaction gas (leakage of fuel gas to the cathode side 104b, leakage of oxidant gas to the anode side 104a, leakage of reaction gas outside the MEA 105, etc.), between the opposing anode-side separator 106a and the cathode-side separator 106b, a pair of opposing gaskets having a gas sealing function, namely, the anode-side gasket 109a and the cathode-side gasket 109b, are disposed on the peripheral edge of the MEA 105 (the protruding portion P of the polymer electrolyte membrane 101 outside the anode 104a and the cathode 104b).
These anode-side gasket 109a and the cathode-side gasket 109b has, for example, a cross section of a substantially rectangular shape and a continuous annular structure, can be fabricated in a conventionally known manner with a use of, for example, an O-ring, a rubber sheet, a composite sheet of an elastic resin and a rigid resin, etc., and serve to sandwich the foregoing whole protruding portion P of the polymer electrolyte membrane. In view of the easiness in handling of the MEA 105, gaskets made of a composite material having a certain degree of rigidity are usually used in integration with the MEA 105.
As a result of disposing the anode-side gasket 109a and the cathode-side gasket 109b as described above such that the foregoing whole protruding portion of the polymer electrolyte membrane 101 is sandwiched by these gaskets, one closed-space enveloping the anode 104a is formed by the anode-side separator 106a, the polymer electrolyte membrane 101 and the anode-side gasket 109a; and another closed-space enveloping the cathode 104b is formed by the cathode-side separator 106b, the polymer electrolyte membrane 101 and the cathode-side gasket 109b. These closed-spaces serve to prevent leakage of reaction gas supplied to the anode 104a and the cathode 104b. 
It should be noted that in the case where the anode-side gasket 109a and the cathode-side gasket 109b are disposed in the foregoing position, there inevitably occurs a working tolerance, an assembling tolerance, etc. of the component parts. It is therefore extremely difficult to bring the anode-side gasket 109a and the cathode-side gasket 109b in sufficiently close contact with the end face of the anode 104a and the cathode 104b, respectively. Accordingly, as shown in FIGS. 10 to 12, in the case where the anode-side gasket 109a and the cathode-side gasket 109b are disposed in the foregoing position, gaps are easily formed between the anode-side gasket 109a and the anode 104a, and between the cathode-side gasket 109b and the cathode 104b (i.e., a anode-side gap 110a and a cathode-side gap 110b).
If the anode-side gap 110a and the cathode-side gap 110b as described above are formed, a case may occur in which the reaction gas leaks into the anode-side gap 110a and the cathode-side gap 110b. In another case, part of the reaction gas fails to flow into the interior of the anode 104a and the cathode 104b, and moves through the anode-side gap 110a and the cathode-side gap 110b and is discharged outside the MEA 105. This disadvantageously has made it extremely difficult to maintain an effective power generation performance.
In addition, when fabricating a stacked-type fuel cell stack, the anode-side gap 110a and the cathode-side gap 110b have been provided intentionally from the design stage in order to prevent the anode-side gasket 109a and the cathode-side gasket 109b from overlapping with the anode 104a and the cathode 104b, for the purpose of improving the productivity. For this reason also, it has been difficult to eliminate the anode-side gap 110a and the cathode-side gap 110b. 